A&P Chapter 24 - Digestive System - Part 2

Lactose

Primary sugar in milk

Lactase

Brush border enzyme that digests lactose

Lactose Intolerance

Characterized by diarrhea, gas, bloating, and abdominal cramps after ingesting milk and other dairy products

Diarrhea occurs because the undigested lactose causes fluid retention in the small intestine

Gas, bloating, and cramps occur when bacteria break down the lactose anaerobically

Celiac Disease

Autoimmune response against a protein called gluten, which is naturally found in grains such as wheat, barley, and rye

Presence of gluten in the small intestine results in an inflammatory response, which damages villi and microvilli of small intestine

Can lead to abdominal pain, diarrhea, and malnutrition

Accessory Organs

Pancreas

Liver

Gallbladder

Pancreas Location

Behind the stomach

Pancreatic Juice

Produced by pancreatic cells

Enter duodenum via pancreatic duct

*contains sodium bicarbonate and digestive enzymes

Pancreas

Endocrine gland

Secretes insulin when blood glucose levels rise

Type I Diabetes

Not enough insulin

Normally diagnosed in childhood

Type II Diabetes

Body's cells are insulin-resistant

Normally occurs in adulthood

Risk factors: obesity, inactivity, family history

Liver - Structure and Location

Largest gland in the body

Lies mainly in upper right abdominal cavity, under diaphragm

Lobules

Structural and functional units of liver

*filter blood in liver and remove poisonous substances

Hepatic Portal Vein

Brings blood to liver from GI tract

Liver Functions

1. Destroys old red blood cells; excretes bilirubin

2. Detoxifies blood by removing and metabolizing poisonous substances

3. Stores iron, water-soluble vitamin B12, and the fat-soluble vitamins A, D, E, and K

4. Makes plasma proteins, such as albumins and fibrinogen, from amino acids

5. Stores glucose as glycogen after a meal; breaks down glycogen to glucose to maintain the glucose concentration of blood between eating periods

6. Produces urea after breaking down amino acids

7. Helps regulate blood cholesterol level, converting some to bile salts

Liver

Stores vitamins

Involved in blood glucose homeostasis

Produces plasma proteins

Regulates blood cholesterol levels

Blood Glucose Homeostasis

Stores glucose as glycogen

When blood glucose is low, it releases glucose by breaking down glycogen

Converts glycerol and amino acids to glucose

As amino acids are converted to glucose, urea is formed

Bile

Contains bile salts, water, cholesterol, and bicarbonate

Contains bilirubin

Bilirubin

Green pigment formed from the breakdown of hemoglobin

Where is Bile Produced?

Liver

Where is Bile Stored?

Gallbladder

Gallbladder

Pear-shaped organ just below liver

Gallstones

Made of stone-like material in gallbladder

Liver Disorders

Hepatitis

Cirrhosis

Jaundice

Jaundice

Caused by liver disease leaking bile pigments into blood

Yellowish tint to whites of eyes and skin

Hepatitis

Inflammation of liver

3 Major Forms of Hepatitis

Hep A

Hep B

Hep C

Hepatitis A

Usually acquired from sewage-contaminated drinking water and food

Hepatitis B

Usually from sexual contact, but also from blood transfusions or contaminated needles

More contagious than the AIDS virus and is spread in the same way

*Vaccines are available for hepatitis A and B.

Hepatitis C

Usually acquired by infected blood

Can lead to chronic hepatitis, liver cancer, and death.

Cirrhosis

Chronic disease

Liver becomes fatty, and filled with fibrous scar tissue

What People is Cirrhosis Often Seen in?

People with obesity and alcohol use disorder, due to malnutrition and the excessive alcohol (a toxin) the liver is forced to break down

When can the Liver Regenerate or Recover?

If the rate of regeneration exceeds the rate of damage

*During liver failure there may not be enough time to let the liver heal so will need a liver transplantation

What Controls Secretion of Digestive Juices?

Nervous system and digestive hormones

What Nervous System Stimulates Gastric Secretion?

Parasympathetic

Gastrin

Hormone produced by stomach from a meal rich in protein

Increases the secretory activity of gastric glands

Secretin

Secreted by the duodenum

Release is stimulated by HCl (present in chyme)

Cholecystokinin (CCK)

Released by duodenum when proteins and fat are present

Causes liver to increase production of bile and causes gallbladder to contract and release stored bile

What Hormones Increase Production of Pancreatic Juice?

Secretin and Cholecystokinin (CCK)

Parts of Large Intestine

Cecum

Colon

Rectum

Anal Canal

Large Intestine Structure

Larger in diameter but shorter in length

Cecum

First portion of large intestine

Vermiform Appendix

Projection off of cecum

Fights infections

Appendicitis

Inflammation of appendix

*can cause peritonitis

Peritonitis

Life-threatening infection of peritoneum

Parts of Colon

Ascending Colon

Transverse Colon

Descending Colon

Sigmoid Colon

Rectum

Last portion of large intestine

Opens at anus

Anus

Where defecation occurs

Defecation

Expulsion of feces

Peristalsis forces feces into rectum

Stretching of rectal wall initiates nerve impulses to spinal cord

Rectal muscles contract and anal sphincters relax, allowing feces to exit body through the anus

Can inhibit defecation by contracting the external anal sphincter, which is made of skeletal muscle

Large Intestine Functions

Does not produce digestive enzymes

Does not absorb nutrients except certain vitamins

Absorbs water from feces to prevent dehydration

Absorbs vitamins produced by intestinal flora

Forms feces

Intestinal Flora

Bacteria that inhabit the intestine

*break down indigestible material and produce B-complex vitamins and vitamin K

Feces

¾ water, ¼ solid wastes

Bacteria and dietary fiber (indigestible remains) make up the solid wastes

Bacteria digesting indigestible materials causes odor of feces and accounts for gas

Stercobilin

Breakdown product of bilirubin, and oxidized iron

Causes brown color of feces

Diarrhea

Increased peristalsis and failure to absorb water from feces, due to either an infection or nervous stimulation

Constipation

Dry, hard feces

May be controlled with water and fiber

Hemorrhoids

Enlarged, inflamed blood vessels of the anus due to chronic constipation, pregnancy, aging, anal intercourse

Diverticulosis

Pouches; weak spots in the muscularis layer.

Irritable Bowel Syndrome (IBS) or Spastic Colon

Muscularis contracts powerfully but without normal coordination

Symptoms of IBS

Abdominal cramps, gas, constipation, and urgent, explosive stools

Inflammatory Bowel Disease (IBD)

Includes Ulcerative Colitis and Crohn's disease

Ulcerative Colitis

Affects large intestine and rectum

Results in diarrhea, rectal bleeding, abdominal cramps, and urgency to defecate

Crohn's Disease

Usually in the small intestine

Ulcers in the intestinal wall; painful and bleed as they erode the submucosal layer, where there are nerves and blood vessels

Can't absorb nutrients in the affected areas

Symptoms of Crohn's Disease

Diarrhea, weight loss, abdominal cramping, anemia, bleeding, and malnutrition

Polyps

Small growths in colon lining

Can be benign or cancerous

If colon cancer is detected while still confined to a polyp, the expected outcome is a complete cure

Increased dietary fat raises the risk of colon cancer

Fiber in the diet inhibits colon cancer, and regular elimination reduces the time that the colon wall is exposed to cancer-promoting agents in the feces